This is an improvement in the invention described in U.S. Pat. No. 5,248,566 issued Sep. 28, 1993, the disclosure of which is herein incorporated by reference.
Fuel cells are being developed for use in automotive propulsion systems as alternatives for the internal combustion engine in buses, vans, passenger cars and other four wheel vehicles. The major motivations for developing fuel cell powered vehicles are low emissions of pollutants, high fuel energy conversion efficiencies, superior acceleration, low noise and vibration and the possible use of coal or biomass derived alcohols rather than petroleum-base fuels. Although petroleum based fuels can also be used. The present invention is directed most specifically to systems for using methanol as a fuel.
The two most important operational requirements for a stand-alone fuel cell power system for a vehicle are the ability to start-up quickly and the ability to supply the necessary power and demand for the dynamically fluctuating load. The rapid start-up requirement is obvious.
Alcohols such as methanol are likely fuels for use in fuel cells for transportation applications. Methanol is a commodity chemical that is manufactured from coal, natural gas and other feed stocks, while ethanol is often produced from grain. For use in a fuel cell, however, alcohol must first be converted (reformed) to a hydrogen rich gas mixture. The desired features for such a fuel reformer include rapid start-up, good dynamic response, fuel conversion, small size and weight, simple construction and operation and low cost.
Methanol has been used in steam reforming for providing a hydrogen rich gas stream from mobile combustion engines, see Koenig et al. U.S. Pat. No. 4,716,859 and water, as a reaction product from a fuel cell, has been recycled for use in steam reforming of methanol, see Baker U.S. Pat. No. 4,365,006. Steam reforming of methanol is endothermic and complicates, by its energy requirements, its use in a vehicle. Supplying the hydrogen rich gas on demand in an intermittent variable demanding environment is also a difficult requirement to meet and has been addressed by Ohsaki et al. U.S. Pat. No. 4,988,580 but this suggestion is not applicable to a small, mobile system. The catalytic exothermic partial oxidation-reforming of fuels to produce hydrogen-rich gas streams is known, see Rao U.S. Pat. No. 4,999,993. The use of a partial oxidation reformer had not been used in a vehicle to accomplish the purposes of this invention prior to the disclosure of the Kumar et al. '566 patent which is satisfactory for its intended purposes, but was based on theoretical considerations.
The subject invention is an improvement of that disclosed in the Kumar et al. '566 patent and relates to the use of specific reactor designs and catalyst along with mechanism for controlling the oxygen to methanol mole ratio to control operating temperatures to produce a commercially viable system.